1. Field of the Invention
The invention relates to a source follower and an electronic system utilizing the same.
2. Description of the Related Art
High gain analog amplifiers are typically high impedance and connect a load, such as a capacitor comprising high capacitance or a resistor comprising low impedance. When the load is a resistor comprising low impedance, a voltage buffer is disposed between the analog amplifier and the load for maintaining high gain effect. The voltage buffer refers to a source follower.
FIG. 1 is a schematic diagram of a conventional source follower. Source follower 100 comprises transistors 110 and 120. Transistors 110 and 120 are coupled between voltage sources Vdd and Vss. The gate of transistor 110 receives an input signal Vin and the source thereof provides an output signal Vout. Transistor 120 is served as a current source.
The size of transistor 110 is equal to that of transistor 120 for arriving to a voltage following effect. When the current flowing transistor 110 is equal to the current flowing transistor 120, the voltage difference between the gate and the source of transistor 110 is equal to the voltage difference between the gate and the source of transistor 120. Because the voltage difference between the gate and the source of transistor 120 is equal to zero, the voltage difference between the gate and the source of transistor 110 is also equal to zero. Thus, the output signal Vout is close to the input signal Vin.